DESCRIPTION

The wsdisplay driver is an abstraction layer for display devices within
the wscons(4) framework. It attaches to the hardware specific display
device driver and makes it available as text terminal or graphics inter-
face.
A display device can have the ability to display characters on it
(without help of an X server), either directly by hardware or through
software drawing pixel data into the display memory. Such displays are
called "emulating", the wsdisplay driver will connect a terminal emula-
tion module and provide a tty-like software interface. In contrary, non-
emulating displays can only be used by special programs like X servers.
The console locator in the configuration line refers to the device's use
as output part of the operating system console. A device specification
containing a positive value here will only match if the device is in use
as system console. (The console device selection in early system startup
is not influenced.) This way, the console device can be connected to a
known wsdisplay device instance. (Naturally, only "emulating" display
devices are usable as console.)
The logical unit of an independent contents displayed on a display (some-
times referred to as "virtual terminal") is called a "screen" here. If
the underlying device driver supports it, multiple screens can be used on
one display. (As of this writing, only the vga(4) and the VAX "smg"
display drivers provide this ability.) Screens have different minor dev-
ice numbers and separate tty instances. One screen possesses the "focus",
this means it is displayed on the display and its tty device will get the
keyboard input. (In some cases, if no screen is set up or if a screen was
just deleted, it is possible that no focus is present at all.) The focus
can be switched by either special keyboard input (typically CTL-ALT-Fn)
or an ioctl command issued by a user program. Screens are set up or
deleted through the /dev/ttyCcfg control device (preferably using the
wsconscfg(8) utility). Alternatively, the compile-time option
WSDISPLAY_DEFAULTSCREENS=N will set up N screens of the display driver's
default type and using the system's default terminal emulator at autocon-
figuration time.
In addition and with help from backend drivers the following features are
also provided:
• Loading, deleting and listing the loaded fonts.
• Browsing backwards in the screen output, the size of the buffer for
saved text is defined by the particular hardware driver.
• Blanking the screen by timing out on inactivity in the screen holding
the input focus. Awakening activities consist of:
• pressing any keys on the keyboard;
• moving or clicking the mouse;
• any output to the screen.
Blanking the screen is usually done by disabling the horizontal sync
signal on video output, but may also include blanking the vertical
sync in which case most monitors go into power saving mode. See
wsconsctl(8) for controlling variables.
Consult the back-end drivers' documentation for which features are sup-
ported for each particular hardware type.

BUGS

The wsdisplay code currently limits the number of screens on one display
to 8.
The terms "wscons" and "wsdisplay" are not cleanly distinguished in the
code and in manual pages.
"non-emulating" display devices are not tested.
MirOS BSD #10-current February 29, 2004 1